Compositions and methods for protecting a plant from an insect pest are provided. The invention provides mutagenized nucleic acids that have been engineered to encode pesticidal polypeptides having increased resistance to proteolytic degradation by a plant protease. In particular, nucleic acid sequences encoding pesticidal polypeptides modified to comprise a proteolytic protection site that confers resistance to degradation or proteolytic inactivation by a plant protease are provided. Particular embodiments of the invention provide pesticidal polypeptide compositions and formulations, expression cassettes, and transformed plants, plant cells, and seeds. These compositions find use in methods for controlling pests, especially plant pests. Novel plant proteases, sequences encoding these proteases, and methods for their use are also provided.